1. Field of the Invention
The present invention relates to an energy dispersion type fluorescent X-ray type thickness measurement device having the merits of being both multi-elemental and non-destructive and being for use in film thickness management in the surface processing industry such as the plating and sputtering of films.
2. Background Information
In the related art, the film composition in surface processing is already known, so energy dispersion type fluorescent X-ray film thickness measurement devices are utilized in production lines with the purpose of quality management, which incurs the limitation that it is difficult to increase measuring time This means that a higher count rate is required using the energy resolution, which means utilizing mainly fluorescent X-ray film thickness measurement devices utilizing proportional counting tubes. However, in the case of utilization in research and development, accuracy and sensitivity are more important than putting restraints on measuring time. For this purpose, fluorescent X-ray film measurement devices mounted with Si (Li) semiconductor detectors or PIN diode detectors have been utilized because they demonstrate superior energy resolution.
FIG. 5 shows an example of a related art fluorescent X-ray film thickness measuring device. A high voltage is applied from an X-ray generation high voltage source 1. Primary X-ray 3 emitted from an X-ray tube 2 are then irradiated onto a sample 5 by means 4 for focusing onto a microscopic unit using a slit, collimator, or capillary utilizing a total reflection phenomena. A sample observation mirror 6 and a sample observation optical system 7 are provided for positioning of the measurement locations by movement of the sample 5 through control of a stage 19 by a control and computing section 17. Fluorescent X-rays 8 generated by the sample are detected by an energy dispersion-type sensor 9. A pre-amplifier 10 is provided to receive an output of the sensor 9. A pre-amplifier 10 is provided to receive an output of the sensor 9 and a linear amplifier 11 receives the output of the pre-amplifier, which is supplied to a frequency analyzer (MCA) 12 with an output signal thereof being quantitatively processed by a control and computing section 17.
Further, a recent tendency is to employ microscopic parts in surface processing units. This means providing collimators for converging and irradiating X-rays and an optical sample monitoring system for confirming where X-rays are being irradiated from. FIG. 7A and FIG. 7B show examples of two different types of sample irradiating systems of the related art. In FIG. 7A, a half mirror and a collimator block are located at the same height in such a manner that an X-ray irradiation axis and an optical sample monitoring axis coincide. In FIG. 7B, a half mirror is located below the collimator block.
The energy dispersion detector has a detection performance whereby the resolution and the count rate conflict with each other. Typically, when the device thickness and surface area of the sensor are increased in order to increase the count rate, the resolution either deteriorates or does not function at all.
Conventionally, a proportional counter tube is typically employed when carrying out film thickness measurements on thin films using a fluorescent X-ray film thickness measurement device. Accurate film thickness and composition measurements are possible without performing special processing providing that the atomic numbers of the elements making up the thin film and materials (substrate) are separable to a certain extent when using a proportional counter tube. However, when the atomic numbers are separated into the neighboring nickel (Z=28) and zinc (Z=29), there is a problem that the peaks to be counted overlap with each other, which needs to be remedied. For example, there is a secondary filtering method whereby a thin plate of cobalt (Z=27) is inserted prior to detection and peak separation is achieved by utilizing the difference in results for absorption of copper, and a digital filtering method which provides peak separation by performing numerical operation on the shapes of the peaks. The secondary filtering is limited to appropriate combinations. This is therefore effective in the case of dedicated function but is not appropriate in cases where the object is to take measurements for various combinations. The digital filtering method is capable of being applied to various combinations but there are problems with stability compared with secondary filtering methods that accompany peak separation errors.
If peak separation is demanded, it is possible to use an Si (Li) semiconductor detector with superior energy resolution. However, when an Si (Li) semiconductor detector is utilized, it is necessary to periodically supply liquid nitrogen as a coolant, which causes problems with respect to both costs and operation. PIN diode detectors that employ Peltier cooling are therefore adopted to resolve this problem of supplying liquid nitrogen, but this causes a substantial deterioration in the energy resolution. This is, however, limited to low energy X-ray applications due to the detection rate in principle being poor with respect to high-energy X-rays.
Moreover, optical sample monitoring systems have the following problems.
FIG. 8 shows a conceptual view of broadening of an X-ray irradiation beam when a collimator is used. As shown in FIG. 8, when a distance L1 from the end of the collimator to the sample is made long, there is substantial broadening of the X-ray beam, and it is therefore necessary to shorten the length L1 in order to implement a microscopic beam.
With an optical sample monitoring system, with the method of locating the half mirror below the collimator block shown in FIG. 7B, the distance between the device body consisting of the collimator block and the mirror, and the sample, is made long and it is ensured that the sample does not come into contact with the device body. However, when this distance is made long, the actual dimensions of the irradiation also become large. This means that broadening is substantial even if a small collimator is prepared, which makes implementation of a microscopic beam difficult. As shown in FIG. 7A, when the purpose is to implement a microscopic beam, a half mirror is located at the position of the collimator block, a still image display saved prior to taking measurements is taken when measurements are to be taken, and the distance between the sample and the collimator is made small. As the purpose of taking measurements with a microscopic portion is on the whole materials which do not have projections, such as wafers, there is no chance of damage being incurred by the device body through contact with the sample even if the distance between the sample and the collimator is small.
However, as cases of measuring vehicle parts and electronic components etc. which have projections with a normal beam size are common, it is preferable to obtain a real image of the location currently being measured rather than having a still image. This causes inconveniences with the collimator block of the structure shown in FIG. 7A. In order to resolve the above situation, the present invention sets out to tackle the problem of measuring a broad range of materials in a manner compatible with low energy to high energy fluorescent X-rays.
According to the present invention, counting is performed simultaneously using a two system X-ray detector by dividing the energy regions in such manner that a PIN diode detector of superior energy resolution is utilized for low energy regions where X-ray energies are close to each other and a proportional counter tube or CdZnTe detector with a superior count rate but with poor resolution for high energy regions is utilized when the count rate is poor using the PIN diode detector high resolution is not required.
Further, the distance is made short between the collimator and the sample when a microscopic beam is utilized. A half mirror is positioned at the same height as the collimator at a side surface of the collimator. The position is then decided upon using the half mirror. Movement in a horizontal direction is then performed so that a prescribed collimator approaches and irradiation using a microscopic beam then takes place, with a still image taken prior to taking measurements being displayed during measurement. When a normal beam is utilized, a second collimator block is provided above the half mirror, with a real image provided by the half mirror then being visible during measurement.